Not Federally Funded: The research leading to this invention was not Federally Funded.
No Microfiche or other type of program is included in this application.
1. Field of the Invention
Liquid level within a tank means theine of transition from liquid to vapor since there is substantially always vapor residing above any liquid body. The discussion of optical detection of liquid level through a sight glass or window by a device or detector always means the discrimination by the detector positioned on one side of the window between the characteristics of vapor and the characteristics of liquid positioned on the other side of the window. Most sight glasses or windows that are provided for visual monitoring of liquid level in a tank or vessel, such as a compressor crankcase, consist of two substantially planar parallel sides, one facing the liquid-vapor side and one facing the outside. Prior art designs directed to detecting a change from vapor to liquid have either employed floats immersed in the liquid for situating a switch or have employed a window with a prism formed in the liquid-vapor side of the window to interact with a light source and light sensor or transducer for returning to the transducer a high percentage of the light emitted by the light source when only vapor was present on the prism side of the window and for returning very little light to the transducer when only liquid was present on the prism side of the window. Such prism faced windows are not often found on vessel sight glasses.
Therefore this invention is directed toward an optically based liquid level (liquid-vapor) detector for use with a window having a substantially planar side facing the liquid-vapor side and a substantially planar side positioned parallel to the liquid-vapor side facing the outside. The detector comprises a light source positioned on the outside of the window to direct its light through the outside planar side to the inside planar liquid-vapor side and a light detector positioned on the outside of the window to receive light transmitted from the source and returned from the planar liquid-vapor window side. The invention further includes electronic means for detecting the light intensity change affecting the transducer, from the condition of liquid on the liquid-vapor side, to the condition of vapor on the liquid-vapor side of the window, whereby an action or signal can be generated in response to such change.
2. Prior Art
Barbier U.S. Pat. No. 5,072,595 in FIG. 1 teaches a bubble detector for a flow stream having a cavity or chamber positioned above and connected to the flow stream for trapping and accumulating bubbles, the chamber including a window having a prism shape formed on the chamber side and a planar face on the outside and a light emitter 66 directing light through the planar face and toward the prism and a light transducer 68 detecting light returned from the prism. When there is liquid surrounding the prism, little light is returned to the light transducer but when bubbles surround the prism, the prism returns much more light to the transducer. Electronic apparatus detects the light intensity and acts in response thereto. In FIG. 3 Barbier teaches a bubble collecting chamber having a planar face on the chamber side but having a prism shaped face on the outside where the light source 66 directs its light against one outside prism face and the light transducer 68 is positioned to receive light from another prism face. The planar face on the bubble or chamber side acts like a 90 degree prism because the light path from source to transducer impacts the planar face at a 45 degree angle and, in the absence of liquid or the presence of bubbles is reflected from the planar face at a 45 degree angle.
Barbier U.S. Pat. No. 5,276,426 teaches only a liquid-vapor discriminator having a window having a prismatic face on the liquid-vapor side and a outer planar face. A light source delivers its light from the outer planar face to the inner prism face where light is reflected in greater or lesser intensity from the prism face to a light detector adjacent the outer planar face.
Harding U.S. Pat. No. 4,354,180 teaches a liquid-vapor discriminating optical device where a window is positioned adjacent the liquid-vapor chamber. The window has a conical or prismatic face on its inner or liquid-vapor side and a substantially planar face on the outside. A light source is positioned on the outside directed primarily against the planar face and a light transducer is positioned on the outside adjacent another position on the planar face where a transition from vapor to liquid on the prism side of the window changes the fraction of light emitted by the light source that is reflected to the light transducer. Reflecting means are also taught that provide a substantially constant light return from source to transducer that acts as a reference.
A primary objective is to provide an economical optical liquid level sensing construction where the glass aperture or window has a flat internal surface in contact with the liquid and vapor instead of a more expensive conical prism-shaped surface in contact with the liquid level being sensed.
A second primary object is to provide an optical-electronic liquid level sensor assembly that can be installed adjacent a window or sight glass in a vessel which is primarily positioned to provide visual indication from the outside of the vessel of the presence inside the vessel of liquid or vapor at the window.
A further object is to proved such a sensor that employs an LED as the light emitter or source and a Darlington Transistor unit as the light transducer or detector.
A further object is to provide such a level sensor assembly which operates effectively when the window has a non-prismatic planar surface facing the liquid-vapor side.
A further object is to provide such a level sensor assembly when the window has a non-prismatic planar surface facing the outside.
A further object is to provide such a level sensor assembly when the window planar liquid-vapor or inside surface is substantially parallel to the outside planar surface.
A further object is to provide such a level sensor where the axis"" of the light emitter and the light transducer are parallel and substantially perpendicular to the plane of the outside window surface.
A further object is to provide such a level sensor where the light emitter and the light sensor are close to each other and separated by an opaque light barrier.
A further object is to provide such a level sensor where the axis"" of the light emitter and the light transducer converge at a point on the liquid-vapor inside surface of the window.
An assembly, including a walled vessel having a window, for opto-electrically differentiating between the presence of liquid and vapor within the vessel at the window, the window having a planar interior face and a planar exterior face substantially parallel with the planar interior face and further providing an electrically actuated light source outside the window positioned to direct light toward the outside surface of the window and an electrically reactive light sensor outside the window positioned to receive light from the source reflected from the window inside surface, the reflected light having a greater intensity on the presence of vapor at the window interior and lesser intensity on the presence of liquid at the window interior and electrical means for reacting differently to the greater and the lesser reflected light intensity.